Using inductors in electric power systems for transmission of electrical energy is known. Electric power systems in this connection mean systems for voltages exceeding 1 kilo-volt and inductors mean stationary induction machines such as reactors and transformers.
When an inductor is short-circuited, the cable winding of the inductor is subjected to axial and radial short-circuit forces. The radial forces in the inductor act outwards and bring about tensile stresses on the cable that constitutes the winding in the inductor. The axial forces in the inductor act upwards/downwards and bring about shearing stresses on the cable. When the inductor is short-circuited, both these types of mechanical stresses may lead to the cable being damaged. To avoid this, it is desirable, in cable-wound induction machines such as reactors and transformers, to protect the cable winding, for example by clamping the winding or minimizing the short-circuit forces.
WO 98/34243 describes a cable-wound transformer/reactor, where the winding is provided with a number of axially extending spacers, which separate each cable turn in a radial direction in the winding, in order, inter alia, to create axial cylindrical cooling ducts. Further, the spacer according to the embodiment is adapted to axially clamp the winding together into a uniform winding subassembly.
However, WO 98/34243 is limited to primarily absorbing short-circuit forces acting in the axial direction since no prestress in the radial direction occurs.
WO 99/28923 describes a cable-wound transformer with one high-voltage winding and one low-voltage winding. Here the turns of the high-voltage winding alternate with the turns of the low-voltage winding, in order thus to minimize the short-circuit forces. However, for reactors with one winding only, this method is not applicable.